Coupling device for slot antenna



April 25, 1961 s. J. BAZAN 2,981,947 COUPLING DEVICE FOR SLOT ANTENNA Filed Sept 24, 1957 INVEN TOR. ST EVE-N J. BAZAN F'. Bymdflzgm J 7' Tana Er 2,981,947 r COUPLING DEVICE FOR SLOT ANTENNA Qteven J. Bazan, Philadelphia, Pa., assignor to Radio Corporation ofAmerica, a corporation of Delaware I Filed Sept. 24, 19s7,'ser.No.6ss,92o

' ZClaims. or. 343-767 j j The invention relates to a'coupling device, and particular'ly to a coupling device for'slot antennas or for slotted transmission lines. a

An object of the invention is to provide. an improved coupling device for use with a slot antenna. Another object-of the invention is to provide an im- Uni sd S a s Patent proved coupling device for use 'with slotted transmission lines.

Another object ofthe inventionis to provide an ultrahigh frequency (UHF) antenna system capable of handling large amounts of power, for'example, in the order of a plurality of megawatts of eifectiveradiated power. The coupling device is designed to be used with a hollow 6r coaxial transmission line having a slot in its wall, and provides improved means for coupling radio frequencyenergy between the interior of the transmission line and the surrounding space; Such a transmission line is frequently used as a 'slot' antenna Briefly, the coupling device comprises 'a cylindrically shaped rod-like metallic couplerfas'te'ne'd to the inner surface of the wall of the transmission'linei The coupler is positioned adja- {cent one edge of the slot so, that its long dimension is substantially parallel to thato'ne edge. If the transmission line is to be used to radiate radio frequency energy t to the surrounding space, thepresence of the coupler disturbs the exciting field within the transmissionline so as to provide a radiating fieldacross the slot to the surrounding space. In a like manner, the coupler can a t he used to provide a field within the transmissionline that the transmission line can be used'to receive rad1o frequency energy from the surrounding space. The length of the coupler is made to approach the length of the slot so that for a total amountof radiating field through or across the slot, excess disturbance to the ex- Citing field is avoided. p j

The invention is explained in detail in connection with the accompanying drawing in which;

Figures 1 and 1a show longitudinal views of slotted coaxial transmission line radiators orantennasutilizing the invention;

Figure 2 shows a transverse cross-sectional view taken along the lines 2-2 in Figure l; j Figure 3 shows a perspective view of the'coupler shown in Figures l, 1a and 2; j p I Figure 4 shows .a transverse. cross-sectional view of a slotted hollow transmission line radiator or antenna utilizing the invention, and Figures 5 and 5a show modificationsof the arrangement shown in Figures 1', 1a and 2.'

In Figure 1 a slotted coaxial transmission line 10 comprises a hollow cylindrical: outer conductor 12 and a concentric inner conductor 14 positioned within the outer conductor 12. The dominantmode for the coaxial transmission line 10 is the TEMinode, and radio frequency energy propagated through the transmission line ltl has"- atransversefelectricfield in radialdirections." An clon [gated or 'rectangnlarly shaped slot -16'is' provided in the outergconductotr 12, :and is positionedwithitsfllonger longitudinally.

edges substantially parallel to the longitudinal axis of the transmission line 10. However, the slot 16 may be oriented in other positions, such as with its longer edges positioned at some angle with respect to the longitudinal axis of the transmission line 10. the slot 16 is indicated, illustratively, ters of a wave length longitudinally.

Practically no voltage will be developed across the slot 16 of the transmission line 10, as described so far, in response to the presence of radio frequency energy in the TEM mode within the transmission line 10. Consequently, no radio frequency energy will be coupled between the interior of the transmission line 10 and the surrounding space. However, in accordance with the invention, a voltage or radiating field may be developed across the slot 16 by means of. an elongated, cylindrically shaped, metallic coupler 18. Although the coupler-18 is shown having a circular cross-sectiomit may alsohave as being three quara polygonal or non-circular curved cross-section. '.The

coupler 18 is located within the transmission line 10, and is fastened to the inner surface of the outer conductor 12 adjacent one of the longer edges of the slot 16. The

coupler 18 is positioned so that its longitudinal axisis substantially parallel to' the one edge of the slot 16. The arrangement ofthe coupler 18 in the transmission line It) is also shown in Figure 2. A perspective view of the coupler 18 is shown in Figure 3. V

When radio frequency energyis propagated through the transmission line 10, the coupler '18 creates a disturbance in the field of this radio frequency energy so that a voltage or radiating field appears across the slot 16. It is preferred that the, length of the coupler11l8 be in the order of 50% to of the length ofjthe slot 16, so that the disturbance to-be exciting field along the length of the transmission line 10 may be held to a minimum. In Fig. 1 the length of the member 18 is indicated, illustratively, .as being one half wave length In other words, the coupler 18 extracts the total amount of radiating field across the slot 16 along a greater length from the feeding transmission line 10 than prior art devices, such as a probe, thus avoiding a point loading. The heavy energy concentration present at a point loading will not only result in a voltage breakdown and hence limited power rating but, in the case of a plurality of slots extending longitudinally along the 7 transmission line 10, will also cause unwanted disturbance in adjacent slots. 7 V

In contrast to this, the coupler 18 of this invention,

while extracting the same total amount of energy, but

'Figure 4 shows a transverse cross-sectional view of a hollow cylindrically shaped transmission line 20 utilizing the invention. The transmission line 20 is provided with an elongated slot 22 similar in shape to the slot 16 shown in Figures 1 and 2.

A cylindrically shaped metallic coupler 18 is fastened to the inner surface of the wallet the transmission line 20 adjacent the slot 22, and is positioned with its longitudinal axis substantially parallel to the one edge of the slot 22. The operation ofthe transmission line shown in Figure 4 is coaxial transmission 1ine'10 While the invention has been described in connection with-hollow and coaxial cylindrically shaped transmission lines," the invention can also be used with other i" transmission li'nes,such-as a slotted rectangular wave,- g ,7

The coirlplifis Of the lli ventiqnjis (mit fi d i i connection with high frequency or ultra-high frequency i InFig. 1 the length of similar to that of the shown in'Figur'es 1 and 2.

cylindrical slot antennas which are designed to radiate radio frequency energy through a plurality of slots. These slots may be positioned in various configurations around the circumference of the antenna as shown in Figure 5, and, above one another in various arrays as shown in Figures 1a and 5. Figure 5a shows a transverse crosssectional view of the arrangement of Figure 5, on the line 5a-5b of Figure 5. With a proper selection of conpler diameter and associated slot length, an independent amplitude control or an independent phase control of the radiated energy may be obtained. -Some antennas may utilize one of the controls. However, in a more general case, the dimensions of the coupler and slot will provide interdependent amplitude and phase controls; If the antenna is provided with a plurality' of slots along its length, different slots may be provided with difiierent diameter and length couplers. Also, if. a plurality of slots are provided at the same level in the antenna, different size and dimensioned couplersmay be used with the different slots to shape the radiated pattern, so as to ,favor one direction over another. Thus, the'invention,can

provide any desired amplitude and phase of the energy radiated from any of the slots. In addition, since the couplers provide a means for radiating energy from the exciting field over a greater length than previous devices,

their power handling capacity is limited only to the extent of the power handling capacity of the transmission line itself.

An antenna comprising a coaxial transmission line -having cylindrical inner and outer conductors was constructed in accordance with the invention with the following specifications:

Frequency: 629 megacycles 0uter conductor: 12.820 inches inside diameter Inner conductor: 8.268 inches outside diameter Couplers: Solid aluminum, M2 long and 0.5-1.6 inches.

in diameter effective radiated power of one megawatt when excited by a transmitter delivering a rated power of 25 kilowatts.

What is claimed is:

1. Apparatus for translating radio frequency energy through an elongated slot opening in the outer member of two coaxial members, said elongated slot having a length not to materially exceed 3M 4, said apparatus comprising an elongated conductive member fastened to the inner wall of said outer coaxial member at one side of the said elongated slot opening with one side of said members long dimension substantially parallel to and substantially registered with said one side of said elongated slot, said conductive member having a length of the order of A/ 2, where A is the RF wave length.

2. Apparatus for translating radio frequency energy through an elongated slot opening in the outer member of two coaxial members, said members being capable of presenting a transverse electric field in radial directions upon excitation by radio frequency energy, said elongated slot having a length not to materially exceed 3M4, said apparatus comprising an elongated conductive member positioned with respect to the inner wall of said outer coaxial member to cooperate with one side of the said elongated slot opening and with one side of said members long dimension substantially parallel to and substantially registered with said one side of said elongated slot whereby to create a disturbance in said field so that a radiating field appears. across said slot, said conductive member having a length of the order of M2, where A is the RF wave length.

References Cited in the file of this patent UNITED STATES PATENTS 2,477,510 Chu July 26, 1949 2,574,433 Clapp Nov. 6, 1951 2,600,179 Alford June 10, 1952 2,658,143 Fiet et al. Nov. 3, 1953 2,724,774 Fiet Nov. 22, 1955 2,803,008 Lindenblad Aug. 13, 1957 2,818,565 Ajioka et al. Dec. 31. 1957 

